Like MongoDB or Couchbase, RethinkDB is a clustered, document-oriented database that delivers the benefits of flexible schema, easy development, and high scalability. Unlike those other document databases, RethinkDB supports “real time” applications with the ability to continuously push updated query results to applications that subscribe to changes.

In this case, a “real time” application is one that must support a large flow of client requests that alter the state of the database and keep all clients apprised of those changes. A common example of a real-time application is the multiplayer game: Hundreds or thousands of users are pushing buttons, those button pushes are changing the game state, and all of the users must see all of the changes in real time.